1. Field of the Invention
This invention relates to cleaning heat exchanger tubes. More particularly, it relates to improved apparatus that is coupled to the ends of a heat exchanger tube to capture a brush or sponge that is propelled back and forth through the tube by reversible fluid pressure.
2. Description of the Prior Art
A common type of heat exchanger has a bundle of tubes which are fixed at their ends in headers or tube sheets. Water or other fluid flows from a common water box or reservoir on one end of the bundle through the tubes to a second common water box or reservoir at the other end of the bundle. Heat exchange is effected through the heat conductive walls of the tubes between the fluid in the tubes and a different temperature water or other fluid on the outside of the tubes. Exemplary of such heat exchangers are the condensors that are widely employed to dispell or recover heat from waste process steam in industrial and electric generating plants. In these condensors, cooling water, which often is untreated, is pumped through the tubes to condense the steam on the outer surface of the tubes. As is well known, if the cooling water is untreated or inadequately treated to prevent the precipitation of dissolved minerals, a mineral deposit will gradually accumulate on the inside of the tubes.
Such mineral deposit, which is commonly known as scale, impairs heat exchange efficiency and may lead to corrosion of the tubes. It must, therefore, be removed regularly. An effective means of doing so is to employ the circulating cooling water to propel a cleaning element, such as a tube brush or sponge, through each tube to dislodge the deposit and permit it to become suspended in the water and carried away in the discharge.
U.S. Pat. No. 3,319,710 describes a tube cleaning system which is applicable to condensors or other heat exchangers in which the cooling water flow is reversible. An elongated brush is placed within each tube and a tubular monolithic molded synthetic resin chamber, which has an inside diameter that is less than the length of the brush, is attached to each end of the tube to capture the expelled brush and hold it in remote alignment with its tube until the water flow is reversed. Water passes through the chamber via perforations in its wall and through an opening, which is restricted to prevent passage by the brush, in the end of the chamber distal from the heat exchanger tube. When the water flow is reversed, the brush is driven back into and through the heat exchanger tube and is captured in the chamber at the opposite end.
A major disadvantage of this system is the fact that the restricted end of the chamber does not permit easy insertion of an electronic probe into the heat exchanger tube to test the tube wall integrity, as required by modern maintenance practice for heat exchangers. When these monolithic plastic chambers are cemented to the heat exchanger tube, as is customary with non-cupreous tubes, the most practical way that this maintenance can be done is to break the chamber away and replace it with a new one when the test is completed.
One means of avoiding this problem is disclosed in U.S. Pat. No. 4,124,065, which describes a thin metal brush capturing chamber that is expanded with a roller expander into leakproof engagement with the end of a heat exchanger tube. Access to the tube is provided by a removable restriction in the end of the chamber distal from the tube. While this eliminates the necessity of replacing the brush catching chambers after each test, it is awkward and difficult to pass a probe through the thin metal chamber without bending that chamber or damaging the probe on its sharp edges. In addition, there is a substantial risk of damage to the end of the heat exchanger tube when it does become necessary to remove a bent or otherwise damaged chamber and expand a new chamber into that tube.
A second means of avoiding the necessity of replacing brush capturing chambers after each tube test also is disclosed in U.S. Pat. No. 4,124,065. This second means utilizes a thin metal thimble, one end of which is expanded with a roller expander into leakproof engagement with a heat exchanger tube. A thread is formed at the other end of the thimble with a thread roller. The brush capturing chamber is a helically wound wire cage having one fully open end that can be screwed onto the thimble thread. While this removable wire cage eliminates the awkwardness of passing a probe through a thin metal brush capturing chamber, the probe is still subject to damage by the sharp edge at the threaded end of the thimble. The thin metal thimble also must be replaced frequently as it is easily dented or otherwise distorted by insertion of the probe or by repeated removal and reinstallation of the wire cage. The risk of damage to the end of the heat exchanger tube in expanding a replacement thimble into it is undiminished. In addition, the threaded coupling of the thimble and wire cage often becomes loosened by vibrations normally occurring in an operating heat exchanger, which may lead to loss of the cage and brush in the water box.